g,
with two engines of 120 horsepower, each driving propellers of 13 feet
diameter. This was the most successful of the early German dirigibles;
it made a number of voyages with a dozen passengers in addition to its
crew, as well as proving its value for military purposes by use as
a scout machine in manoeuvres. Later Parsevals were constructed
of stream-line form, about 300 feet in length, and with engines
sufficiently powerful to give them speeds up to 50 miles an hour.

Major Von Gross, commander of a Balloon Battalion, produced semi-rigid
dirigibles from 1907 onward. The second of these, driven by two 75
horse-power Daimler motors, was capable of a speed of 27 miles an hour;
in September of 1908 she made a trip from and back to Berlin which
lasted 13 hours, in which period she covered 176 miles with four
passengers and reached a height of 4,000 feet. Her successor, launched
in April of 1909, carried a wireless installation, and the next to this,
driven by four motors of 75 horse-power each, reached a speed of 45
miles an hour. As this vessel was constructed for military purposes,
very few details either of its speed or method of construction were made
public.

Practically all these vessels were discounted by the work of Ferdinand
von Zeppelin, who set out from the first with the idea of constructing
a rigid dirigible. Beginning in 1898, he built a balloon on an aluminium
framework covered with linen and silk, and divided into interior
compartments holding linen bags which were capable of containing nearly
400,000 cubic feet of hydrogen. The total length of this first Zeppelin
airship was 420 feet and the diameter 38 feet. Two cars were rigidly
attached to the envelope, each carrying a 16 horse-power motor, driving
propellers which were rigidly connected to the aluminium framework of
the balloon. Vertical and horizontal screws were used for lifting and
forward driving and a sliding weight was used to raise or lower the stem
of the vessel out of the horizontal in order to rise or descend without
altering the load by loss of ballast or the lift by loss of gas.

The first trial of this vessel was made in July of 1900, and was
singularly unfortunate. The winch by which the sliding weight was
operated broke, and the balloon was so bent that the working of the
propellers was interfered with, as was the steering. A speed of 13 feet
per second was attained, but on descending, the airship ran against
some piles and was fur